Thermal shutdown is utilized as one of several possible mechanisms for protecting integrated circuits (ICs) from high operating temperatures, such as may occur at high current loads or other high power dissipation events. To implement desired protection, thermal shutdown control circuitry can be located near expected high power dissipation regions of an IC. The thermal shutdown control circuitry usually includes a PTAT (proportional to absolute temperature) circuit, such as a current PTAT (or IPTAT) circuit. The IPTAT circuit provides an output current that is proportional to the absolute temperature of the components constituting the circuit. The output current can be utilized to drive associated detection circuitry that provides a control signal for implementing thermal shutdown and disabling the affected components of the functional circuitry.
While thermal shutdown control circuitry is routinely utilized in many types of integrated circuits, the operation of thermal shutdown control circuitry is not routinely tested in the normal course of IC fabrication. This is because proper testing generally would require raising the temperature of the IC device to the thermal shutdown activation temperature. For example, one might physically raise temperature of the device, such as by placing the device in an oven, while testing the associated protection circuitry to determine whether the device properly disables. In addition to the added stress on the IC device, by implementing such a test on a frequent basis would prove time consuming. As a result, such an approach is generally cost prohibitive for most fabrication processes since device yield could significantly decrease.
Accordingly, rather than testing operation of the thermal detection circuitry, most existing test procedures operate to determine whether the associated protection mechanism functions properly. These approaches typically control and override thermal shutdown signal, such that the protection circuitry, when operating properly, is activated to disable the functional circuitry in the device. However, these approaches provide no quantitative mechanism to ascertain at what temperature the protection will become active.